termios(3C) termios(3C)
NAME
termios: tcgetattr, tcsetattr, tcsendbreak, tcdrain, tcflush,
tcflow, cfgetospeed, cfgetispeed, cfsetispeed, cfsetospeed,
tcgetpgrp, tcsetpgrp, tcgetsid - general terminal interface
SYNOPSIS
#include <termios.h>
int tcgetattr(int fildes, struct termios *termios_p);
int tcsetattr(int fildes, int optional_actions,
const struct termios *termios_p);
int tcsendbreak(int fildes, int duration);
int tcdrain(int fildes);
int tcflush(int fildes, int queue_selector);
int tcflow(int fildes, int action);
speed_t cfgetospeed(const struct termios *termios_p);
int cfsetospeed(struct termios *termios_p, speed_t speed);
speed_t cfgetispeed(const struct termios *termios_p);
int cfsetispeed(struct termios *termios_p, speed_t speed);
#include <sys/types.h>
#include <termios.h>
pid_t tcgetpgrp(int fildes);
int tcsetpgrp(int fildes, pid_t pgid);
pid_t tcgetsid(int fildes);
DESCRIPTION
These functions describe a general terminal interface for
controlling asynchronous communications ports. A more
detailed overview of the terminal interface can be found in
termio(7), which also describes an ioctl(2) interface that
provides the same functionality. However, the function
interface described here is the preferred user interface.
Many of the functions described here have a termios_p argument
that is a pointer to a termios structure. This structure
contains the following members:
tcflag_t c_iflag; /* input modes */
tcflag_t c_oflag; /* output modes */
tcflag_t c_cflag; /* control modes */
tcflag_t c_lflag; /* local modes */
cc_t c_cc[NCCS]; /* control chars */
These structure members are described in detail in termio(7).
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termios(3C) termios(3C)
Get and Set Terminal Attributes
The tcgetattr function gets the parameters associated with the
object referred by fildes and stores them in the termios
structure referenced by termios_p. This
function may be invoked from a background process; however,
the terminal attributes may be subsequently changed by a
foreground process.
The tcsetattr function sets the parameters associated with the
terminal (unless support is required from the underlying
hardware that is not available) from the termios structure
referenced by termios_p as follows:
If optional_actions is TCSANOW, the change occurs
immediately.
If optional_actions is TCSADRAIN, the change occurs
after all output written to fildes has been transmitted.
This function should be used when changing parameters
that affect output.
If optional_actions is TCSAFLUSH, the change occurs
after all output written to the object referred by
fildes has been transmitted, and all input that has been
received but not read is discarded before the change is
made.
The symbolic constants for the values of optional_actions are
defined in termios.h.
Line Control
If the terminal is using asynchronous serial data
transmission, the tcsendbreak function causes transmission of
a continuous stream of zero-valued bits for a specific
duration. If duration is zero, it causes transmission of
zero-valued bits for at least 0.25 seconds, and not more than
0.5 seconds. If duration is not zero, it behaves in a way
similar to tcdrain.
If the terminal is not using asynchronous serial data
transmission, the tcsendbreak function sends data to generate
a break condition or returns without taking any action.
The tcdrain function waits until all output written to the
object referred to by fildes has been transmitted.
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termios(3C) termios(3C)
The tcflush function discards data written to the object
referred to by fildes but not transmitted, or data received
but not read, depending on the value of queue_selector:
If queue_selector is TCIFLUSH, it flushes data received
but not read.
If queue_selector is TCOFLUSH, it flushes data written
but not transmitted.
If queue_selector is TCIOFLUSH, it flushes both data
received but not read, and data written but not
transmitted.
The tcflow function suspends transmission or reception of data
on the object referred to by fildes, depending on the value of
action:
If action is TCOOFF, it suspends output.
If action is TCOON, it restarts suspended output.
If action if TCIOFF, the system transmits a STOP
character, which causes the terminal device to stop
transmitting data to the system.
If action is TCION, the system transmits a START
character, which causes the terminal device to start
transmitting data to the system.
Get and Set Baud Rate
The baud rate functions get and set the values of the input
and output baud rates in the termios structure. The effects
on the terminal device described below do not become effective
until the tcsetattr function is successfully called.
The input and output baud rates are stored in the termios
structure. The values shown in the table are supported. The
names in this table are defined in termios.h.
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termios(3C) termios(3C)
Name Description Name Description
____________________________________________
B0 Hang up B600 600 baud
B50 50 baud B1200 1200 baud
B75 75 baud B1800 1800 baud
B110 110 baud B2400 2400 baud
B134 134.5 baud B4800 4800 baud
B150 150 baud B9600 9600 baud
B200 200 baud B19200 19200 baud
B300 300 baud B38400 38400 baud
cfgetospeed gets the output baud rate stored in the termios
structure pointed to by termios_p.
cfsetospeed sets the output baud rate stored in the termios
structure pointed to by termios_p to speed. The zero baud
rate, B0, is used to terminate the connection. If B0 is
specified, the modem control lines are no longer asserted.
Normally, this disconnects the line.
cfgetispeed returns the input baud rate stored in the termios
structure pointed to by termios_p.
cfsetispeed sets the input baud rate stored in the termios
structure pointed to by termios_p to speed. If the input baud
rate is set to zero, the input baud rate is specified by the
value of the output baud rate. Both cfsetispeed and
cfsetospeed return a value of zero if successful and -1 to
indicate an error. Attempts to set unsupported baud rates are
ignored. This refers both to changes to baud rates not
supported by the hardware, and to changes setting the input
and output baud rates to different values if the hardware does
not support this.
Get and Set Terminal Foreground Process Group ID
tcsetpgrp sets the foreground process group ID of the terminal
specified by fildes to pgid. The file associated with fildes
must be the controlling terminal of the calling process and
the controlling terminal must be currently associated with the
session of the calling process. pgid must match a process
group ID of a process in the same session as the calling
process.
tcgetpgrp returns the foreground process group ID of the
terminal specified by fildes. tcgetpgrp is allowed from a
process that is a member of a background process group;
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termios(3C) termios(3C)
however, the information may be subsequently changed by a
process that is a member of a foreground process group.
If there is no foreground process group, tcgetpgrp returns a
value greater than 1 that does not match the process group ID
of any existing process group.
Get Terminal Session ID
tcgetsid returns the session ID of the terminal specified by
fildes.
Return Values
On success, tcgetpgrp returns the process group ID of the
foreground process group associated with the specified
terminal. On failure, tcgetpgrp returns -1 and sets errno to
identify the error.
On success, tcgetsid returns the session ID associated with
the specified terminal. On failure, tcgetsid returns -1 and
sets errno to identify the error.
On success, cfgetispeed returns the input baud rate from the
termios structure.
On success, cfgetospeed returns the output baud rate from the
termios structure.
On success, all other functions return 0. On failure, they
return -1 and set errno to identify the error.
Errors
In the following conditions, all of the functions fail and set
errno to:
EBADF The fildes argument is not a valid file
descriptor.
ENOTTY The file associated with fildes is not a
terminal.
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termios(3C) termios(3C)
tcsetattr also fails if the following is true:
EINVAL The optional_actions argument is not a proper
value, or an attempt was made to change an
attribute represented in the termios structure
to an unsupported value.
tcsendbreak also fails if the following is true:
EINVAL The device does not support the tcsendbreak
function.
tcdrain also fails if one or more of the following is true:
EINTR A signal interrupted the tcdrain function.
EINVAL The device does not support the tcdrain
function.
tcflush also fails if the following is true:
EINVAL The device does not support the tcflush
function or the queue_selector argument is not
a proper value.
tcflow also fails if the following is true:
EINVAL The device does not support the tcflow function
or the action argument is not a proper value.
tcgetpgrp also fails if the following is true:
ENOTTY the calling process does not have a controlling
terminal, or fildes does not refer to the
controlling terminal.
EINTR A signal interrupted the tcgetpgrp function.
tcsetpgrp also fails if the following is true:
EINVAL pgid is not a valid process group ID .
ENOTTY the calling process does not have a controlling
terminal, or fildes does not refer to the
controlling terminal, or the controlling
terminal is no longer associated with the
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termios(3C) termios(3C)
session of the calling process.
EPERM pgid does not match the process group of an
existing process in the same session as the
calling process.
tcgetsid also fails if the following is true:
EACCES fildes is a terminal that is not allocated to a
session.
REFERENCES
setpgid(2), setsid(2), termio(7)
NOTICES
Considerations for Threads Programming
Open file descriptors are a process resource and available to
any sibling thread; if used concurrently, actions by one
thread can interfere with those of a sibling.
While one thread is blocked, siblings might still be
executing.
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